1. Field of the Invention
The present invention relates to a pressure sensor comprising a sensor channel system having at least one measurement opening and comprising at least one detector arranged to perform a measurement indicative of the pressure at the at least one measurement openings.
2. Background Information
Many automated manufacturing processes require the sensing of the distance between a manufacturing tool and the product or material surface being worked. In some situations, such as semiconductor lithography, the distance must be measured with accuracy approaching a nanometer.
The challenges associated with creating a proximity sensor of such accuracy are significant, particularly in the context of photolithography systems. In the photolithography context, in addition to being non-intrusive and having the ability to precisely detect very small distances, the proximity sensor can not introduce contaminants or come in contact with the work surface, typically a semiconductor wafer. Occurrence of either situation may significantly degrade or ruin the semiconductor quality.
Different types of proximity sensors are available to measure very small distances. Examples of proximity sensors include capacitance and optical gauges. These proximity sensors have serious shortcomings when used in photolithography systems because physical properties of materials deposited on wafers may impact the precision of these devices. For example, capacitance gauges, being dependent on the concentration of electric charges, can yield spurious proximity readings in locations where one type of material (e.g., metal) is concentrated. Another class of problems occurs when exotic wafers made of non-conductive and/or photosensitive materials, such as Gallium Arsenide (GaAs) and Indium Phosphide (InP), are used. In these cases, capacitance and optical gauges may provide spurious results.
U.S. Pat. No. 4,953,388, entitled Air Gauge Sensor, issued Sep. 4, 1990 to Andrew Barada (“'388 Patent”), and U.S. Pat. No. 4,550,592, entitled Pneumatic Gauging Circuit, issued Nov. 5, 1985 to Michel Deschape (“'592 Patent”), disclose an alternative approach to proximity sensing that uses an air gauge sensor. U.S. Pat. Nos. 4,953,388 and 4,550,592 are incorporated herein by reference in their entireties. These sensors use reference and measurement nozzles to emit an air flow onto reference and measurement surfaces and measure back pressure differences within the sensors to measure the distance between the measurement nozzle and the measurement surface.
Furthermore, principles of pneumatic gauging are discussed in Burrows, V. R., The Principles and Applications of Pneumatic Gauging, FWP Journal, October 1976, pp. 31-42, which is incorporated herein by reference in its entirety. An air gauge sensor is not vulnerable to concentrations of electric charges or electrical, optical and other physical properties of a wafer surface. Current semiconductor manufacturing, however, requires that proximity is gauged with high precision on the order of nanometers. Earlier versions of air gauge sensors, however, often do not meet today's lithography requirements for precision.
Air gauges proximity sensors operate on the principle that changes in back pressure of a nozzle close to a surface can be set up to be proportional to changes in the distance to the surface. This process involves supplying pressurized air to the device, and then blowing that air out a nozzle and against the surface to be measured.
The resist used in microlithography are sensitive to the atmospheric environment. Often, the air needs to be specially conditioned in order to keep the resist in the proper chemical state. Additionally, the sensing systems (often interferometers) used to control the stages the wafers ride on can also be very sensitive to the content and temperature of the air they work in. Complex air conditioned supplies are developed to meet these needs inside microlithography equipment. Different wavelengths also require different chemical criteria, which can require altering a sensor's infrastructure.
The gas used within a gas gauge proximity sensor must be carefully conditioned so as not to interfere with the chemical or sensing systems. Maintaining the chemical and thermal properties of the gas can be difficult. Similar considerations and operational challenges impact proximity sensors used within immersion lithography systems.
What are needed are systems and methods for diminishing the challenges associated with maintaining the chemical and thermal properties of the gas or liquid used within a gas gauge or liquid flow proximity sensor.